Combustion instabillity reduction device



Dec. 26, 1967 D. LEWIS 7 COMBUSTION INSTABILITY REDUCTION DEVICE Filed Jan. 26, 1965 55 XX f4 /////r/7ae 650K966 & (5W4? United States Patent 3,359,737 COMBUSTION INSTABILITY REDUCTION DEVICE George D. Lewis, North Palm Beach, Fla., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Jan. 26, 1965, Ser. No. 428,110 7 Claims. (Cl. 60265) This invention relates to a combustion instability reduction device and particularly for the reduction of instability which may develop in the combustion chamber of a rocket engine.

One object of this invention is to provide acoustic damping adjacent the walls of a combustion chamber.

Another object of this invention is to provide a combustion chamber with a perforated wall with a back-up chamber to reduce combustion instability.

A further object of this invention is to provide a combustion chamber having walls formed of tubes with openings, said tubes forming part of the instability reduction device.

Another object of this invention is to have adjacent tubes predimpled so that the adjacent tubes when positioned to form a combustion chamber have their dimples co-act to form passages through the tube wall chamber.

A further object of this invention is to provide a pressure shell around the exterior of the combustion chamber having end plates with the combustion chamber so that a chamber is formed which will act as a Helmholtz resonator.

Another object of this invention is to provide a coolant flow passing through the tubes to provide cooling.

A further object of this invention is to provide a combustion chamber with a plurality of holes of predetermined size comprising a predetermined total area, and providing a back-up resonant chamber having a wall located around said combustion chamber a predetermined distance away for its entire circumference.

Another object of this invention is to provide additional cooling when necessary by admitting a coolant into the chamber around the combustion chamber and permitting it to flow out through the holes into the combustion chamber.

Other objects and advantages will be apparent from the specification and claims and from the accompanying drawings which illustrate an embodiment of the invention.

FIGURE 1 is a side view of a rocket engine, partially in section, showing the combustion chamber and resonant chamber.

FIGURE 2 is an enlarged view showing a group of tubes taken from the combustion chamber as shown in FIG. 1.

FIGURE 3 is an enlarged view taken along the line 3-3 of FIG. 2.

FIGURE 1 shows a rocket engine 2 having a nozzle assembly 4, a combustion apparatus 6 and an injector head 8. The nozzle assembly 4 comprises an inner member 10 which has its inner surface formed to the desired contour of the nozzle throat while helical lands 18 extend around its outer periphery forming grooves 20, said lands extending from approximately one end to the other. The exit end of the nozzle is formed having a flange 22 which extends outwardly from the rear end of the inner member 10. The forward or inlet end of the nozzle 4 is for-med having a circular series of grooves 26 to receive a plurality of ends of tubes 100 for a purpose to be hereinafter described.

Two semicircular members 30 are positioned over the inner member 10 forming passageways A with grooves 20. These members 30 while having their inner surface each contoured to meet with the contour of the member 10 at the ends of the lands 18, have their outer surfaces 36 each formed to be semicylindrical with a semicylindrical flange 44. When assembled, the surfaces 36 form a cylindrical face with an annular flange formed of the two halves 44. A flange 32 extends rearwardly from the inner edge of each semicircular member 30. This flange 32 and the ends of the semicircular members 30 form an annular groove 34 with the radially extending flange 22 of the inner member 10.

A cylindrical cover member 40 is placed around the semicircular members 30 and has an annular notch 42 which mates with flanges 44 on the semicircular portions. An annular flange 46 extends outwardly from this end of the cover member 40 for a purpose to be hereinafter described. The annular groove 34 becomes an annulus with the inner surface of cover member 40, connected to the free ends of the passageways A at the rear end of the nozzle. The free end of the flange 22 meets the under part of the rearward inner end of the cylindrical cover member 40 and is fixed thereto.

the inner member 10 and ring-like plate 50, each extending inwardly approximately half way. This plate 50 is bolted to the flange 46 by bolts 52 to hold the nozzle assembly in position and connect the combustion apparatus 6 and nozzle assembly 4 together. In this assembled position, the forward ends of the passageways A are connected to the ends of tubes to permit flow therebetween.

The ends 104 of the tubes 100 are arranged to fit into a circular series of openings 54 formed in the face of an annular rear member 56. The member 56, while being annular, can be constructed in any manner well known in the prior art, one construction would form the member of a forward and rearward half. A cylindrical member 58 is placed around the annular ring of tubes 100 with its one end fixed, as by brazing, to ring-like plate 50 where it meets it, and the other end is fixed in a similar manner to the outer circumference of member 56 at 60. This construction forms resonant chamber 59, bounded by outer cylindrical member 58, the inner combustion chamber absorber wall, and the end members 50 and 56.

The tubes 100 which form the cylindrical wall of the combustion chamber of the combustion apparatus 6 have holes 101 located between adjacent tubes to provide passages between the main combustion chamber and the resonant chamber 59 formed by the tubes 100, cylindrical member 58, ring-like plate 50 and annular ring member 56'. This makes the combustion chamber wall an absorber wall. The holes 101 are formed by placing a semicircular dimple in adjacent tubes so that they will cooperate when the tubes are fixed together, thus, completing a passage. When the number and size of holes for a given combustion chamber has been determined, the tubes can all be properly dimpledj and with their ends fixed in a jig to hold them in the circular manner desired for the main combustion chamber, the tubes are then brazed so that they will be held together leaving the holes 101 the desired size. Once this cylindrical ring of tubes has been formed, it can be fixed in the rocket engine as set forth above.

An external circular manifold 62 encircles the member 56 and is connected to an internal annular manifold 64 formed in the lower part of the member 56 by a plurality of tubes 66 and passageways 68 in member 56. A tube 70 directs flow away from the manifold 62. The passageways 68 and tubes 66 are made of such size to carry the flow through the tubes 100. The injector head 8 can be of any known design and directs propellants into said chamber formed by tubes 100.

A coolant supply 150 is connected by a conduit 152 to the annulus formed by the annular groove 34 and inner surface of cover member 40. The conduit 152 extends through the cover member 40. Valve means 154 is placed along the conduit 152 to control flow from the coolant supply. A coolant supply is also connected to the chamber 59 formed around the main combustion chamber by a conduit 162. This conduit extends through the cylindrical member 58. A valve means 164 is connected in conduit 162 to control the flow of coolant therethrough. This valve means 164 can be actuated by a temperature probe located somewhere within the combustion chamber or nozzle to automatically initiate a fiow of coolant therethrough when necessary.

It can be seen that propellants will be injected into the combustion chamber from the injector head 8 so that they will ignite therein. The products of combustion will be directed to the nozzle assembly 4 to be exhausted therefrom. While the rocket engine is operating, the coolant supply will pass through conduit 152 with valve 154 open and flow through the annular groove 34 into the rear ends of the grooves 20 between the lands 18 and then flow into the ends 102 of the tubes 100. This flow will then cool the tubes 160 and pass into the internal annular manifold 64. From this manifold it will pass radially outwardly through passageways 68 and tubes 66 into the external circular manifold 62. From this manifold the coolant can be redirected to the coolant supply 150 or if a propellant has been used for cooling it can be directed to the injector head 8 to be used for ignition.

When extreme temperatures are reached at some area within the combustion chamber or nozzle, the valve means 164 can be turned on and a coolant will be directed to chamber 59 and flow through holes 161 to provide film cooling along the inside of the combustion chamber and nozzle.

Most engines that experience combustion instability produce chamber pressure fluctuations at a predominant frequency that is related to the acoustic resonant modes of the chamber. Typical examples are the first tangential mode and first longitudinal mode. Radial modes and higher harmonics are also encountered. The basic mode frequencies can be approximately calculated as follows: first tangential,

first radial,

first longitudinal,

where f=predominant frequency of instability c=speed of sound of gas medium in combustion chamber R=combustion chamber radius X=combustion chamber length from injector to nozzle The frequencies of pressure disturbance can also be obtained by the use of pressure recording equipment which is placed to record pressure fluctuations within the combustion chamber. This reference has been made to the chamber pressure fluctuations because a knowledge of the frequency of these fluctuations is needed for solving the following formulae. Having a combustion chamber design, the geometric dimensions of the absorbing or resonant chamber of a combustion instability reduction device can be determined by solving the following formula with values of D, L, l and 0', to obtain the highest value of a, the absorption coefficient, defined as the fraction of incident energy absorbed. This coefficient is calculated by Where 0, the specific acoustic resistance is calculated by w op owwum 0 10 and Q, the quality factor is determined by (3) i 9a'C where l the eflective length of the acoustic mass is figured by and f resonant frequency of the absorber is determined by Listed below are the symbols set forth in the formulae above together with their meaning:

c=speed of sound of gas medium in resonant chamber D=diameter of openings in combustion chamber absorber wall f=frequency of pressure disturbance in combustion chamber f =resonant frequency of the resonant chamber L=depth of resonant chamber around combustion chamber l=length of openings in combustion chamber absorber wall l =effective length of the openings in combustion chamber absorber wall Q=quality factor a=absorbtion coeflicient e=nonlinear resistance factor =specific acoustic resistance u=1bsolute viscosity of gas medium in resonant chamber =mass density of gas medium in resonant chamber a=absorber open area ratio, percent open area of combustion chamber absorber wall w =angular resonant frequency of resonant chamber w=angular frequency of pressure disturbance in combustion chamber In solving the formulae set forth above to arrive at a high value of a for specific values of D, L, l and 0', Formula 4 is solved directly since all symbol values are known. Formula 5 can then be solved since all of its values are known. Formula 2 is solved directly using values of 5 obtained from empirical correlations relating e to particle velocity and/or particle displacement as shown in the following references:

(1) On the Theory and Design of Acoustic Resonators by Uno Ingard, pp. 1037-1061 in The Journal of the Acoustical Society of America of November 1953.

(2) Efifect of -Nonlinear Losses on the Design of Absorbers for Combustion Instabilities by A. W. Blackman, pp. 10224028 of the American Rocket Society Journal of November 1960'.

Formula 3 can then be solved since all of its values are now known.- The values of 6, Q, j, and f are then placed in Formula 1 and this formula is solved to arrive at 01. As stated hereinbefore, the values of D, L, l and aare varied until the highest value of 0c is obtained.

With reference to the Helmholtz resonator, this resonator is discussed in Chapter 8 of the Fundamentals of Acoustics by Kinsler and Frey.

Referring again to the method of making the perforated chamber wall with a plurality of tubes, the dimples or crimps can be formed by any means desired so as to obtain a side profile as viewed in FIG. 2 with the dimple depth being made /2D. Each tube is crimped so that meeting sides of adjacent tubes will have identical crimping spacing whereby each crimp on one side of one tube cooperates with a crimp on the mating side of the adjacent tube to form the perforations or holes 101. When the tube assembly is brazed together the braze material is permitted to fill in the grooved area a predetermined amount as at 105 between holes 101 of adjacent tubes and from each end hole 101 to its respective tube ends 102 or 104 of the assembly. This fill in (see FIG. 3) provides the l for the holes 101 and the D in the lengthwise plane betwen tubes. While the brazing is being done, the holes are maintained their proper D. If any hole becomes clogged or restricted it can be made its proper size by drilling or by any other method known in the art.

Although only one embodiment of this invention has been illustrated and described herein, it will be apparent that various changes and modifications may be made in the construction and arrangement of the various parts without departing from the scope of this novel concept.

I claim:

1. In combination, a combustion chamber, means for forming combustion products in said chamber, means for directing a ifow of combustion products from said combustion chamber, said combustion chamber having a substantially cylindrical Wall, said cylindrical Wall being formed of a plurality of tubes being placed closely together and having side-to-side engagement, said wall having openings therein, said openings being formed between adjacent tubes, each pair of adjacent tubes being fixed together along its length except where an opening appears, a resonant chamber located around said combustion chamber.

2. In combination, a combustion chamber, means for forming combustion products in said chamber, means for directing a flow of combustion products from said combustion chamber, said combustion chamber having a substantially cylindrical wall, said cylindrical wall being formed of a plurality of tubes with crimps on two sides being placed closely together and having side-to-side engagement, said wall having openings therein, said openings being formed between adjacent tubes by mating crimps, each pair of adjacent tubes being fixed together along its length except where an opening appears, a resonant chamber located around said combustion chamber.

3. In combination, a combustion chamber, means for forming combustion products in said chamber, means for directing a flow of combustion products from said combustion chamber, said combustion chamber having a substantially cylindrically wall, said cylindrical wall being formed of a plurality of tubes being placed closely together and having side-to-side engagement, said wall having openings therein, said openings being formed between adjacent tubes, each pair of adjacent tubes being fixed together along its length except where an opening appears, a resonant chamber located around said combustion chamber, a coolant supply, means connecting said coolant supply to ends of said plurality of tubes, means directing said coolant supply away from the other ends of said tubes.

4. In combination, a combustion chamber, means for forming combustion products in said chamber, means for directing a flow of combustion products from said combustion chamber, said combustion chamber having a substantially cylindrical wall, said cylindrical wall being formed of a plurality of tubes with crimps on two sides being placed closely together and having side-to-side engagement, said wall having openings therein, said openings being formed between adjacent tubes by mating crimps, each pair of adjacent tubes :being fixed together along its length except where an opening appears, a resonant chamber located around said combustion chamber, a coolant supply, means connecting said coolant supply to said tubes.

5. In combination, a combustion chamber, means for forming combustion products in said chamber, nozzle means for directing a flow of combustion products from said combustion chamber, said combustion chamber having :a substantially cylindrical wall, said cylindrical Wall being formed of a plurality of tubes with crimps on two sides being placed closely together and having side-toside engagement, said wall having openings therein, said openings being formed between adjacent tubes by mating crimps, each pair of adjacent tubes being fixed together along its length except where an opening appears, a resonant chamber located around said combustion chamber, a coolant supply, first means connecting said coolant supply to said tubes, second means connecting said coolant supply to said resonant chamber to provide film cooling for the combustion chamber and nozzle means.

6. In combination, a combustion chamber, means for forming combustion products in said chamber, nozzle means for directing a flow of combustion products from said combustion chamber, said combustion chamber having a substantially cylindrical wall, said cylindrical wall being formed of a plurality of tubes with crimps on two sides being placed closely together and having sideto-side engagement, said wall having openings therein, said openings being formed between adjacent tubes by mating crimps, each pair of adjacent tubes being fixed together along its length except where an opening appears, a resonant chamber located around said combustion chamber, a coolant supply, first means connecting said coolant supply to said tubes, second means connecting said coolant supply to said resonant chamber to provide film cooling for the combustion chamber and nozzle means, said second means having valve means for controlling a flow of coolant from said coolant supply.

7. In combination, a combustion chamber, means for forming combustion products in said chamber, means for directing a flow of combustion products from said combustion chamber, said combustion chamber having a substantially cylindrical wall, said cylindrical wall being formed of a plurality of tubes with crimps on two sides being placed closely together and having side-to-side engagement, said wall having openings therein, said openings being formed between adjacent tubes by mating crimps, each pair of adjacent tubes being fixed together along its length except where an opening appears, said openings having a length l and a diameter D, the total area of the hole openings in the combustion chamber in relation to the closed area being equal to 0-, a resonant chamber located around said combustion chamber, said resonant chamber having a cylindrical wall around said combustion chamber, said wall being located a distance L from the combustion chamber, the values of L, l, D and 0' being such that the absorbtion coefiicient a is the highest.

References Cited UNITED STATES PATENTS 2,793,421 5/1957 Brumbaugh 29157 2,902,823 9/1959 Wagner 60-35.6 2,937,500 5/1960 Bodine 6039.77 3,134,224 5/1964 Lippincott 6035.6 3,208,132 9/1965 Escher 29-157 RALPH D. BLAKESLEE, Primary Examiner.

MARK NEWMAN, BENJAMIN A. BORCHELT,

Examiners. 

1. IN COMBINATION, A COMBUSTION CHAMBER, MEANS FOR FORMING COMBUSTION PRODUCTS IN SAID CHAMBER, MEANS FOR DIRECTING A FLOW OF COMBUSTION PRODUCTS FROM SAID COMBUSTION CHAMBER, SAID COMBUSTION CHAMBER HAVING A SUBSTANTIALLY CYLINDRICAL WALL, SAID CYLINDRICAL WALL BEING FORMED OF A PLURALITY OF TUBES BEING PLACED CLOSELY TOGETHER AND HAVING SIDE-TO-SIDE ENGAGEMENT, SAID WALL HAV- 